So the NFL doesn't allow you to trade "cash considerations" the way other leagues do. That would be the only caveat to any deal.
With that said, there is one way around it, which would be for a player to convert base salary into a signing bonus before a trade, which would accelerate the cap hit onto the current team's cap that season (as well as actual cash paid). I can't remember if I've seen that or not in the NFL specifically, but it is an option.